Some biological reflections on the concept of life.

Life is the natural phenomenon that has always aroused the largest interest of philosophers, theologians and scientists, on which a new science--biology--was founded two century ago just for throwing light on its mechanisms. As the pre-Hellenic culture was not able to separate distinctly philosophy from science, life was interpreted as a spurious flurry of the activity of Nature, in which religion, magic and science were interlaced in an intricate way. The Hippocratic medicine constituted the first attempt to focus attention on life by collecting some biological knowledge in order to maintain man's health. All the subsequent physiologists (from the Hellenic to the Latin period) benefited from the precepts of the Corpus Hippocraticum as long as the Christian religion imposed its theological rules that favoured the question relative to soul ever more closely interlaced with the physiology of body. The concept of life became therefore subjected to a number of opposite theories with strong prevalence of metaphysical conjectures until the 19th century but, in spite of this imposition, splendid successes were achieved by physiologists and naturalists such as Harvey, Descartes, Haller, Malpighi, Spallanzani, Wolff, and others, who laid the foundation of a biology that has Lamarck as promoter. The importance of Lamarck's biology came from the release from metaphysics with the introduction of physical and structural concepts which permeated the experimental biology to come. Three main events characterised the biology of the 19th century: i) the interplay of the new chemistry with biology, ii) the cell theory, iii) the concept of metabolism. These events led biology to the 20th century, the era of biochemistry and molecular genetics. The discoveries relative to metabolism characterised the first half of this century, while the second half was witness to the internal mechanisms regulating the life of cells, perhaps the most advanced success of the biology of all time. Today, the cell is not only the centre of a metabolism that, on the whole, may be regarded as the material basis of life, but it is also the central control of communication in response to a great number of stimuli. May life be considered on the basis of biochemical and molecular genetical bases? The answer to this question depends on the credo of everybody. In any case, these mechanisms may explain "what" life is, whereas "why" life exists is still matter of philosophy, and then a fully open question.